Vehicle control device

ABSTRACT

A vehicle control device which is applicable to a vehicle brake device, controls the pressure increasing control valve and the pressure-decreasing control valve so that an actual servo pressure detected by the servo pressure sensor becomes a target servo pressure; and controls so as to increase the target servo pressure by a predetermined amount, while the brake actuator is executing the braking control which accompanies a brake fluid pumping back control wherein the brake fluid supplied to the wheel cylinder is pumped back to the master cylinder by the built-in pump.

TECHNICAL FIELD

This invention relates to a vehicle control device which is used in a vehicle.

BACKGROUND ART

As one type of a vehicle brake device, a device which is disclosed in a Patent Literature 1 is known. As shown in FIG. 1 of the Patent Literature 1, the vehicle brake device includes a master cylinder 1 wherein master pistons 113 and 114 are driven to move by a servo pressure in a servo chamber 127 and by the movement of the master pistons, master pressure in the master chambers 132 and 136 changes, a mechanical type servo pressure generating device 44 connected to a high pressure source 431 and the servo chamber to generate the servo pressure in the servo chamber corresponding to the pilot pressure generated in a pilot chamber based on the brake hydraulic pressure of the high pressure source, an electric pilot pressure generating device 41, 42, 43 connected to the pilot chamber for generating a desired pilot pressure in the pilot chamber, a master-pilot connecting brake fluid passage 511 which connects the master chamber and the pilot chamber and a brake actuator 53 which performs an ABS control and an ESC control and so on. The master-pilot connecting brake fluid passage is a passage branched from the master-wheel connecting passage 51 which connects the master chamber and the wheel cylinder 541, etc. The vehicle brake device includes a pressure sensor 74 which detects the servo pressure.

In a vehicle brake device as structured above, when a brake pedal 115 is depressed, the brake ECU 6 controls the pressure decreasing valve 41 and the pressure increasing valve 42 in response to the information from the stroke sensor 72. In other words, generally, a target servo pressure is set which corresponds to the stroke amount of the brake pedal 115 and then the pressure decreasing valve 41 and the pressure increasing valve 42 are controlled so that the target servo pressure and the actually detected servo pressure (actual servo pressure) agree with each other (feed-back control).

CITATION LIST

[Patent Literature] Patent Literature 1: JP2013-107562 A

SUMMARY OF INVENTION Technical Problem(s)

However, according to the vehicle brake device as explained above, upon execution of ABS control, if the brake actuator 53 is operated, the flow that the brake fluid is returned to the master cylinder side from the wheel cylinder side and the flow that the brake fluid is supplied to the wheel cylinder side from the master cylinder side are repeated. This leads to a repetition of retreating and advancing movement of the master piston with a short period of time and the volume of the servo pressure chamber is decreased and increased thereby to frequently change the servo pressure therein (actual servo pressure). If the pressure decreasing valve 41 and the pressure increasing valve 42 are controlled in response to the frequent changes of the servo pressure by feedback control, the controlling of the pressure decreasing valve 41 and the pressure increasing valve 42 cannot quickly follow the frequent changes of the servo pressure. Thus, the actual servo pressure cannot be controlled with high responsibility.

Particularly, when the brake fluid is supplied to the wheel cylinder side from the master cylinder side and the master piston advances, there is an anxiety that the servo pressure may not be supplied to the servo pressure chamber with high responsibility. As a result, the actual servo pressure drops relative to the target servo pressure and the master pressure drops to thereby drop the wheel cylinder pressure. This may lead to a drop of actual deceleration relative to the required deceleration.

Accordingly, this invention was made in consideration with the above-mentioned situation and the objective of the invention is to provide a vehicle control device which can surely generate a desired required deceleration without receiving any influence of response delay of servo pressure generation in the vehicle brake device.

Solution to Problem(s)

The brake device according to a first aspect of the invention to solve the above problems is characterized in that in a vehicle control device applicable to a vehicle brake device which includes a master cylinder wherein a master piston is driven to move by a servo pressure in a servo chamber and by the movement of the master piston, a master pressure in a master chamber is changed, a servo pressure generating device formed by a high pressure source, a pressure increasing control valve disposed between the high pressure source and the servo chamber for controlling a flow of a brake fluid from the high pressure source to the servo chamber and a pressure decreasing control valve disposed between a low pressure source and the servo chamber for controlling the flow of the brake fluid from the servo chamber to the low pressure source for generating the servo pressure in the servo chamber in response to an operation of a brake operating member by a driver of a vehicle, a servo pressure sensor configured to detect the servo pressure, a wheel cylinder configured to apply a braking force to a vehicle wheel in response to the master pressure from the master cylinder and a brake actuator disposed between the master cylinder and the wheel cylinder and structured at least so that the brake fluid supplied to the wheel cylinder is pumped back to the master cylinder by a built-in pump, the brake actuator being used for a braking control for controlling a braking force generated by the wheel cylinder. The vehicle control device is configured to control the pressure increasing control valve and the pressure decreasing control valve so that the actual servo pressure detected by the servo pressure sensor becomes a target servo pressure and is configured to control so as to increase the target servo pressure by a predetermined amount, while the brake actuator is executing the braking control which accompanies a brake fluid pumping back control wherein the brake fluid supplied to the wheel cylinder is pumped back to the master cylinder by the built-in pump.

According to the above feature of the invention, while the braking control which accompanies the brake fluid pumping back control wherein the brake fluid supplied to the wheel cylinder is returned to the master cylinder by pumping back operation of the built-in pump, for example, an ABS control, is performed, the target servo pressure is increased by a predetermined amount. Therefore, the actual servo pressure can be increased in response to the increased predetermined amount. Accordingly, during the pressure increasing operation of the ABS control, when the brake fluid is sent to the wheel cylinder side from the master cylinder side due to the advancement of the master piston, a relatively high servo pressure can be supplied to the servo pressure chamber and as a result, without dropping of the master pressure, eventually the wheel cylinder pressure, a deceleration in response to the desired required deceleration can be generated. In other words, the present invention can provide a vehicle control device which can surely generate the desired required deceleration, without receiving any influence of response delay of generation of the servo pressure in the vehicle brake device.

The vehicle control device according to a second aspect of the invention is characterized in that in the first aspect, the predetermined amount is set based on the variation value of the servo pressure derived from a variation of the master pressure generated upon an execution of the braking control which accompanies the brake fluid pumping back control. According to the feature above, during the braking control which accompanies the brake fluid pumping back control (such as during an ABS control), increasing amount of the target servo pressure can be appropriately set to surely supply the servo pressure chamber with a relatively high servo pressure.

The vehicle control device according to a third aspect of the invention is characterized in that in the first or the second aspect, after the execution of the braking control which accompanies the brake fluid pumping back control has been finished, the target servo pressure increased during the execution of the braking control which accompanies the brake fluid pumping back control is decreased based on a ratio of the predetermined amount increased during the braking control which accompanies the brake fluid pumping back control relative to the target servo pressure at an end of the execution of the braking control which accompanies the brake fluid pumping back control. According to the feature above, after the execution of the braking control (such as ABS control) which accompanies the brake fluid pumping back control has been finished, the target servo pressure can be gradually changed to suppress the uncomfortable feeling which the operator of the brake operating member feels.

The vehicle control device according to a fourth aspect of the invention is characterized in that in the first or the second aspect, after the execution of the braking control which accompanies the brake fluid pumping back control has been finished, the target servo pressure increased during the execution of the braking control which accompanies the brake fluid pumping back control is decreased in response to a decrease of an operating amount of the brake operating member. According to the feature above, after the execution of the braking control (such as ABS control) which accompanies the brake fluid pumping back control has been finished, the target servo pressure can be gradually changed to suppress the uncomfortable feeling which the operator of the brake operating member feels.

The vehicle control device according to a fifth aspect of the invention is characterized in that in any one of the first through fourth aspects, an increase of the target servo pressure by the predetermined amount is prohibited until a predetermined time period passes from the end of the execution of the braking control which accompanies the brake fluid pumping back control. According to the feature above, when the braking control which accompanies the brake fluid pumping back control is repeatedly executed for a short period of time (for example, when a vehicle is running on a road, the surface of which has different friction coefficient alternatively, the execution and non-execution of the ABS control are repeatedly performed) a new target servo pressure increase operation is not performed until the predetermined time period passes from the time when the execution of the braking control which accompanies the brake fluid pumping back control finished, even the next braking control which accompanies the brake fluid pumping back control is executed. Thus, an unlimited increase of the target servo pressure can be prevented.

The vehicle control device according to a sixth aspect of the invention is characterized in that in any one of the first through fifth aspects, a total increase amount of the target servo pressure is limited to an increase amount upper limit value when the increase of the target servo pressure is executed. According to the feature above, when the braking control which accompanies the brake fluid pumping back control is repeatedly executed for a short period of time (for example, when a vehicle is running on a road, the surface of which has different friction coefficient alternatively, the execution and non-execution of the ABS control are repeatedly performed) a target servo pressure increase operation is not performed even if the predetermined time period passes from the time when the execution of the braking control which accompanies the brake fluid pumping back control finished, when the total increase amount of the target servo pressure reached to the increase amount upper limit value. Thus, an unlimited increase of the target servo pressure can be prevented.

BRIEF EXPLANATION OF ATTACHED DRAWINGS

FIG. 1 is a conceptual view of the brake device according to an embodiment of the invention;

FIG. 2 is a cross sectional view of a regulator according to the embodiment;

FIG. 3 is a flowchart of a control program (control example) executed by the brake ECU shown in FIG. 1;

FIG. 4 is a time chart showing an operation of the vehicle brake device according to the control example; and

FIG. 5 is a flowchart of another control program (control example) executed by the brake ECU shown in FIG. 1.

EMBODIMENTS FOR IMPLEMENTING INVENTION

The vehicle control device and the vehicle brake device which is controllable by the vehicle control device according to the embodiment of the invention will be explained hereinafter with reference to the attached drawings. It is noted that the same or equivalent components or parts are referenced with the same symbols or the numerals and the shape and the size of each component in the drawings, by which the structural explanation thereof will be made, are not necessarily accurate to the actual product.

As shown in FIG. 1, the brake device is formed by a hydraulic pressure braking force generating device BF which generates the hydraulic pressure braking force and applies the hydraulic pressure braking force to the vehicle wheels 5FR, 5FL, 5RR and 5RL and a brake ECU 6 (corresponding to the vehicle control device) which controls the hydraulic pressure braking force generating device BF.

(Hydraulic Pressure Braking Force Generating Device BF)

The hydraulic pressure braking force generating device BF is formed by a master cylinder 1, a reaction force generating device 2, a first control valve 22, a second control valve 23, a servo pressure generating device 4, a hydraulic pressure control portion 5 and various sensors 71 through 76 and so on.

(Master Cylinder 1)

The master cylinder 1 is a portion which supplies the hydraulic pressure control portion 5 with the brake fluid in response to the operating amount of a brake pedal 10 (brake operating member) and is formed by a main cylinder 11, a cover cylinder 12, an input piston 13, a first master piston 14 and a second master piston 15 and so on. The master cylinder 1 is structured such that the first master piston 14 is driven to move by the servo pressure in the servo chamber 1A and by this movement of the first master piston 14, the master pressure in the first master chamber 1D is changed. It is noted that the first master piston 14 corresponds to the master piston which slidably moves within the master cylinder 1 and generates a master cylinder 1 hydraulic pressure in response to the servo pressure (disclosed in CLAIMS).

The main cylinder 11 is formed in a substantially bottomed cylinder shape housing having a bottom surface closed at a front end and an opening at a rear end thereof. The main cylinder 11 includes therein an inner wall portion 111, which extends inwardly with a shape of flange at a rear side in the inner peripheral side of the main cylinder 11. An inner circumferential surface of the inner wall portion 111 is provided with a through hole 111 a at a central portion thereof. The main cylinder 11 is provided therein at portions closer to the front end than the inner wall portion 111 with a small diameter portion 112 (rear) and a small diameter portion 113 (front), each of which inner diameter is set to be slightly smaller than the inner diameter of the inner wall portion 111. In other words, the small diameter portions 112, 113 project from the inner circumferential surface of the main cylinder 11 having an inwardly annularly shaped profile. The first master piston 14 is provided inside the main cylinder 11 and is slidably movable along the small diameter portion 112 in the axial direction. Similarly, the second master piston 15 is provided inside the main cylinder 11 and is slidably movable along the small diameter portion 113 in the axial direction.

The cover cylinder 12 includes an approximately cylindrical portion 121, a tubular bellow boots 122 and a cup-shaped compression spring 123. The cylindrical portion 121 is arranged at a rear end of the main cylinder 11 and is coaxially fitted into the rear side opening of the main cylinder 11. An inner diameter of a front portion 121 a of the cylindrical portion 121 is formed to be greater than an inner diameter of the through hole 111 a of the inner wall portion 111. Further, the inner diameter of the rear portion 121 b is formed to be smaller than an inner diameter of the front portion 121 a.

The boots 122 is of tubular bellow shaped and is used for dust prevention purpose and is extendible or compressible in front and rearward directions. The front side of the boots 122 is assembled to be in contact with the rear end opening of the cylindrical portion 121. A through hole 122 a is formed at a central portion of the rear of the boots 122. The compression spring 123 is a coiled type biasing member arranged around the boots 122. The front side of the compression spring 123 is in contact with the rear end of the main cylinder 11 and the rear side of the compression spring 123 is disposed with a preload adjacent to the through hole 122 a of the boots 122. The rear end of the boots 122 and the rear end of the compression spring 123 are connected to an operating rod 10 a. The compression spring 123 biases the operating rod 10 a in a rearward direction.

The input piston 13 is a piston configured to slidably move inside the cover cylinder 12 in response to an operation of the brake pedal 10. The input piston 13 is formed in a substantially bottomed cylinder shape having a bottom surface at a front portion thereof and an opening at a rear portion thereof. A bottom wall 131 forming the bottom surface of the input piston 13 has a greater diameter than the diameters of the other parts of the input piston 13. The input piston 13 is arranged at the rear end portion 121 b of the cylindrical portion 121 and is slidably and fluid-tightly movable in an axial direction and the bottom wall 131 is assembled into an inner peripheral side of the front portion 121 a of the cylindrical portion 121.

The operating rod 10 a operable in association with the brake pedal 10 is arranged inside of the input piston 13. A pivot 10 b is provided at a tip end of the operating rod 10 a so that the pivot 10 b can push the input piston 13 toward front side. The rear end of the operating rod 10 a projects towards outside through the rear side opening of the input piston 13 and the through hole 122 a of the boots 122, and is connected to the brake pedal 10. The operating rod 10 a moves in response to the depression operation of the brake pedal 10. More specifically, when the brake pedal 10 is depressed, the operating rod 10 a advances in a forward direction, while compressing the boots 122 and the compression spring 123 in the axial direction. The input piston 13 also advances in response to the forward movement of the operating rod 10 a.

The first master piston 14 is arranged in the inner wall portion 111 of the main cylinder 11 and is slidably movable in the axial direction. The first master piston 14 includes a pressurizing cylindrical portion 141, a flange portion 142 and a projection portion 143 in order from the front and the cylindrical portion 141, the flange portion 142 and the projection portion 143 are formed integrally as a unit. The pressurizing cylindrical portion 141 is formed in a substantially bottomed cylinder shape having an opening at a front portion thereof and a bottom wall at a rear portion thereof. The pressurizing cylindrical portion 141 includes a clearance formed with the inner peripheral surface of the main cylinder 11 and is slidably in contact with the small diameter portion 112. A coil spring-shaped biasing member 144 is provided in the inner space of the pressurizing cylindrical portion 141 between the first master piston 14 and the second master piston 15. In other words, the first master piston 14 is biased by the biasing member 144 towards a predetermined initial position.

The flange portion 142 is formed to have a greater diameter than the diameter of the pressurizing cylindrical portion 141 and is slidably in contact with the inner peripheral surface of the main cylinder 11. The projection portion 143 is formed to have a smaller diameter than the diameter of the flange portion 142 and is slidably and fluid-tightly in contact with the through hole 111 a of the inner wall portion 111. The rear end of the projection portion 143 projects into the inner space of the cylindrical portion 121 passing through the through hole 111 a and is separated from the inner peripheral surface of the cylindrical portion 121. The rear end surface of the projection portion 143 is separated from the bottom wall 131 of the input piston 13 and the separation distance “d” is formed to be variable.

It is noted here that a “first master chamber 1D” is defined by the inner peripheral surface of the main cylinder 11, a front side of the pressurizing cylindrical portion 141 of the first master piston 14 and a rear side of the second master piston 15. A rear chamber which is located further rearward of the first master chamber 1D, is defined by the inner peripheral surface (inner peripheral portion) of the main cylinder 11, the small diameter portion 112, a front surface of the flange portion 142 and the outer peripheral surface of the first master piston 14. The flange portion 142 of the first master piston 14 separates the rear chamber into a front portion and a rear portion and the front portion is defined to be a “second hydraulic pressure chamber 10” and the rear portion is defined to be a “servo chamber 1A” A “first hydraulic pressure chamber 1B” is defined by the inner peripheral surface of the main cylinder 11, a rear surface of the inner wall portion 111, an inner peripheral surface (inner peripheral portion) of the front portion 121 a of the cylindrical portion 121, the projection portion 143 (rear end portion) of the first master piston 14 and the front end of the input piston 13.

The second master piston 15 is coaxially arranged within the main cylinder 11 at a location forward of the first master piston 14 and is slidably movable in an axial direction to be in slidable contact with the small diameter portion 113. The second master piston 15 is formed as a unit with a tubular pressurizing cylindrical portion 151 in a substantially bottomed cylinder shape having an opening at a front portion thereof and a bottom wall 152 which closes the rear end of the tubular pressurizing cylindrical portion 151. The bottom wall 152 supports the biasing member 144 with the first master piston 14. A coil spring-shaped biasing member 153 is disposed in the inner space of the pressurizing cylindrical portion 151 between the second piston 15 and a closed inner bottom surface 111 d of the main cylinder 11. The second master piston 15 is biased by the biasing member 153 in a rearward direction. In other words, the second master piston 15 is biased by the biasing member 153 towards a predetermined initial position. A “second master chamber 1E” is defined by the inner peripheral surface and the inner bottom surface 111 d of the main cylinder 11 and the pressurizing cylindrical portion 151 of the second master piston 15.

Ports 11 a to 11 i, which connect the inside and the outside of the master cylinder 1, are formed at the master cylinder 1. The port 11 a is formed at the main cylinder 11 at a location rearward of the inner wall portion 111. The port 11 b is formed at the main cylinder 11 opposite to the port 11 a at approximately the same location in the axial direction. The port 11 a and the port 11 b are in communication through an annular clearance formed between the inner circumferential surface of the main cylinder 11 and the outer circumferential surface of the cylindrical portion 121. The port 11 a and the port 11 b are connected to a conduit 161 and also connected to a reservoir 171.

The port 11 b is in communication with the first hydraulic pressure chamber 1B via a passage 18 formed at the cylindrical portion 121 and the input piston 13. The fluid communication through the passage 18 is interrupted when the input piston 13 advances forward. In other words, when the input piston 13 advances forward, the fluid communication between the first hydraulic pressure chamber 1B and the reservoir 171 is interrupted.

The port 11 c is formed at a location rearward of the inner wall portion 111 and forward of the port 11 a and the port 11 c connects the first hydraulic pressure chamber 1B with a conduit 162. The port 11 d is formed at a location forward of the port 11 c and the port 11 d connects the servo chamber 1A with a conduit 163. The port 11 e is formed at a location forward of the port 11 d and connects the second hydraulic pressure chamber 10 with a conduit 164.

The port 11 f is formed between the sealing members 91 and 92 provided at the small diameter portion 112 and connects a reservoir 172 with the inside of the main cylinder 11. The port 11 f is in communication with the first master chamber 1D via a passage 145 formed at the first master piston 14. The passage 145 is formed at a location where the port 11 f and the first master chamber 1D are disconnected from each other when the first master piston 14 advances forward. The port 11 g is formed at a location forward of the port 11 f and connects the first master chamber 1D with a conduit 51.

The port 11 h is formed between the sealing members 93 and 94 provided at the small diameter portion 113 and connects a reservoir 173 with the inside of the main cylinder 11. The port 11 h is in communication with the second master chamber 1E via a passage 154 formed at the pressurizing cylindrical portion 151 of the second master piston 15. The passage 154 is formed at a location where the port 11 h and the second master chamber 1E are disconnected from each other when the second master piston 15 advances forward. The port 11 i is formed at a location forward of the port 11 h and connects the second master chamber 1E with a conduit 52.

A sealing member, such as an O-ring and the like (see black dot in the drawings) is appropriately provided within the master cylinder 1. The sealing members 91 and 92 are provided at the small diameter portion 112 and in liquid-tightly contact with the outer circumferential surface of the first master piston 14. Similarly, the sealing members 93, 94 are provided at the small diameter portion 113 and in liquid-tightly contact with the outer circumferential surface of the second master piston 15. Additionally, sealing members 95 and 96 are provided between the input piston 13 and the cylindrical portion 121.

The stroke sensor 71 is a sensor which detects the operating amount (pedal stroke) of the operation of the brake pedal 10 by a driver (operator) of the vehicle and transmits the detected result to the brake ECU 6. A brake stop switch 72 is a switch which detects whether the brake pedal 10 is operated or not by the driver, using a binary signal (ON-OFF) and a detected signal is sent to the brake ECU 6. It may be possible to provide an operating force sensor which detects an operating force (depression force) in response to the operation of the brake pedal 10 by the operator of the vehicle.

(Reaction Force Generating Device 2)

The reaction force generating device 2 is a device which generates a reaction force against the operation force when the brake pedal 10 is depressed and is formed by mainly a stroke simulator 21. The stroke simulator 21 generates a reaction force hydraulic pressure in the first hydraulic pressure chamber 1B and the second hydraulic pressure chamber 1C in response to the operation of the brake pedal 10. The stroke simulator 21 is configured in such a manner that a piston 212 is fitted into a cylinder 211 while being allowed to slidably move therein and a reaction force hydraulic pressure chamber 214 is formed at a location forward side of the piston 212. The piston 212 is biased in the forward side direction by a compression spring 213. The reaction force hydraulic pressure chamber 214 is connected to the second hydraulic pressure chamber 1C via a conduit 164 and the port 11 e, and is connected further to the first control valve 22 and the second control valve 23 via the conduit 164.

When the first control valve 22 is open and the second control valve 23 is closed, a hydraulic pressure circuit “L” is formed by the first hydraulic pressure chamber 1B, the second hydraulic pressure chamber 10, the reaction force hydraulic pressure chamber 214, the conduit 162 and the conduit 164. When the input piston 13 slightly advances by the operation of the brake pedal 10, the fluid communication between the first hydraulic pressure chamber 1B and the passage 18 is interrupted and the fluid communication of the second hydraulic pressure chamber 10 which is connected to the hydraulic pressure circuit “L” with components and passages or conduits other than the second hydraulic pressure chamber 10 is interrupted. Thus the hydraulic pressure circuit L is hydraulically in closed state. By the further advance movement of the input piston 13, the brake fluid in response to the stroke of the input piston 13 is flown into the reaction force hydraulic pressure chamber 214 from the first and the second hydraulic pressure chambers 1B and 10 by overcoming the reaction force of the compression spring 213. Thus, the input piston 13 makes a stroke in response to the operation of the brake pedal 10 and the hydraulic pressure in response to the stroke of the piston 13 is generated in the hydraulic pressure circuit L by the reaction force of the compression spring 213. Such hydraulic pressure is transmitted to the operating rod 10 a and the brake pedal 10 from the input piston 13 and is transmitted to the driver of the vehicle in addition to the reaction force of the compression spring 213 which biases the operating rod 10 a, as a brake reaction force.

(First Control Valve 22)

The first control valve 22 is an electromagnetic valve which is structured to close under non-energized state and opening and closing thereof is controlled by the brake ECU 6. The first control valve 22 is disposed between the conduit 164 and the conduit 162 for communication therebetween. The conduit 164 is connected to the second hydraulic pressure chamber 10 via the port 11 e and the conduit 162 is connected to the first hydraulic pressure chamber 1B via the port 11 c. The first hydraulic pressure chamber 1B becomes in open state when the first control valve 22 opens and becomes in closed state when the first control valve 22 closes. Accordingly, the conduits 164 and 162 are formed for establishing fluid communication between the first hydraulic pressure chamber 1B and the second hydraulic pressure chamber 10.

The first control valve 22 is closed under non-energized state and under this state communication between the first hydraulic pressure chamber 1B and the second hydraulic pressure chamber 10 is interrupted. Due to the closure of the first hydraulic pressure chamber 1B, the brake fluid is nowhere to flow and the input piston 13 and the first master piston 14 are moved integrally keeping the separation distance “d” therebetween to be constant. The first control valve 22 is open under the energized state and under such state, the communication between the first hydraulic pressure chamber 1B and the second hydraulic pressure chamber 10 is established. Thus, the volume change in the first hydraulic pressure chamber 1B and the second hydraulic pressure chamber 10 due to the advancement and retreatment of the first master piston 14 can be absorbed by the transferring of the brake fluid.

The pressure sensor 73 is a sensor which detects the reaction force hydraulic pressure of the second hydraulic pressure chamber 10 and the first hydraulic pressure chamber 1B and is connected to the conduit 164. The pressure sensor 73 detects the pressure of the second hydraulic pressure chamber 10 while the first control valve 22 is in a closed state and also detects the pressure of the first hydraulic pressure chamber 1B while the first control valve 22 is in an open state. The pressure sensor 73 sends the detected signal to the brake ECU 6.

(Second Control Valve 23)

The second control valve 23 is an electromagnetic valve which is structured to open under a non-energized state and the opening and closing thereof is controlled by the brake ECU 6. The second control valve 23 is disposed between the conduit 164 and the conduit 161 for establishing communication therebetween. The conduit 164 is in communication with the second hydraulic pressure chamber 10 via the port 11 e and the conduit 161 is in communication with the reservoir 171 via the port 11 a. Accordingly, the second control valve 23 establishes communication between the second hydraulic pressure chamber 10 and the reservoir 171 under the non-energized state not to generate any reaction force hydraulic pressure but interrupts the communication therebetween to generate the reaction force hydraulic pressure under the energized state.

(Servo Pressure Generating Device 4)

The servo pressure generating device 4 is provided for generating the servo pressure and is formed by a pressure decreasing valve (corresponding to the pressure decreasing control valve) 41, a pressure increasing valve (corresponding to the pressure increasing control valve) 42, a high pressure supplying portion (corresponding to the high pressure source) 43 and a regulator 44 and so on. The servo pressure generating device 4 generates the servo pressure in the servo chamber 1A in response to the operation of the brake pedal 10 by the driver (operator) of the vehicle.

The pressure decreasing valve 41 is a valve structured to open under a non-energized state and the flow-rate thereof is controlled by the brake ECU 6. One end of the pressure decreasing valve 41 is connected to the conduit 161 via the conduit 411 and the other end thereof is connected to the conduit 413. In other words, the one end of the pressure decreasing valve 41 is connected to the reservoir (corresponding to the low pressure source) 171 via the conduits 411, 161 and ports 11 a and 11 b. As stated, the pressure decreasing valve 41 is disposed between the reservoir 171 and the servo chamber 1A and is referred to as a pressure decreasing control valve which controls the flow of the brake fluid from the servo chamber 1A to the reservoir 171.

The pressure increasing valve 42 is a valve structured to close under a non-energized state and the flow-rate thereof is controlled by the brake ECU 6. One end of the pressure increasing valve 42 is connected to the conduit 421 and the other end thereof is connected to the conduit 422. As stated, the pressure increasing valve 42 is disposed between the high pressure supplying portion 43 and the servo chamber 1A and is referred to as a pressure increasing control valve which controls the flow of the brake fluid from the high pressure supplying portion 43 to the servo chamber 1A. The pressure decreasing valve 41 and the pressure increasing valve 42 correspond to a pilot hydraulic pressure generating device.

The high pressure supplying portion 43 is a portion for supplying the regulator 44 mainly with a highly pressurized brake fluid. The high pressure supplying portion 43 includes an accumulator 431, a hydraulic pressure pump 432, a motor 433 and the reservoir 434 and so on. The reservoir 434 is under the atmospheric pressure and is a low pressure source which pressure is lower than the pressure in the high pressure supplying portion 43.

The accumulator 431 is a tank in which a highly pressurized brake fluid is accumulated and is connected to the regulator 44 and the hydraulic pressure pump 432 via a conduit 431 a. The hydraulic pressure pump 432 is driven by the motor 433 and supplies the brake fluid which is reserved in the reservoir 434 to the accumulator 431. The pressure sensor 75 provided in the conduit 431 a detects the accumulator hydraulic pressure in the accumulator 431 and the detected signal is sent to the brake ECU 6. The accumulator hydraulic pressure correlates with the accumulated brake fluid amount accumulated in the accumulator 431.

When the pressure sensor 75 detects that the accumulator hydraulic pressure drops to a value equal to or lower than a predetermined value, the motor 433 is driven on the basis of a control signal from the brake ECU 6, and the hydraulic pressure pump 432 supplies the brake fluid to the accumulator 431 in order to recover a pressure up to the value equal to or more than the predetermined value.

FIG. 2 is a partial cross sectional explanatory view showing the inside of the mechanical type regulator 44 which forms the servo pressure generating device 4. As shown in the drawing, the regulator 44 includes a cylinder 441, a ball valve 442, a biasing portion 443, a valve seat portion 444, a control piston 445 and a sub-piston 446 and so forth.

The cylinder 441 includes a cylinder case 441 a formed in a substantially bottomed cylinder-shape having a bottom surface at one end thereof (at the right side in the drawing) and a cover member 441 b closing an opening of the cylinder case 441 a (at the left side thereof in the drawing). It is noted here that the cylinder case 441 a is provided with a plurality of ports 4 a through 4 h through which the inside and the outside of the cylinder case 441 a are in communication. The cover member 441 b is formed in a substantially bottomed cylinder-shape having a bottom surface and is provided with a cylindrical plurality of ports which is arranged opposite to the respective ports 4 a through 4 h.

The port 4 a is connected to the conduit 431 a. The port 4 b is connected to the conduit 422. The port 4 c is connected to a conduit 163. The conduit 163 connects the servo chamber 1A and the outlet port 4 c. The port 4 d is connected to the conduit 161 via the conduit 414. The port 4 e is connected to the conduit 424 and further connected to the conduit 422 via a relief valve 423. The port 4 f is connected to the conduit 413. The port 4 g is connected to the conduit 421. The port 4 h is connected to a conduit 511, which is branched from the conduit 51.

The ball valve 442 is a valve having a ball shape and is arranged at the bottom surface side (which will be hereinafter referred to also as a cylinder bottom surface side) of the cylinder case 441 a inside of the cylinder 441. The biasing portion 443 is formed by a spring member biasing the ball valve 442 towards the opening side (which will be hereinafter referred to also as a cylinder opening side) of the cylinder case 441 a, and is provided at the bottom surface of the cylinder case 441 a. The valve seat portion 444 is a wall member provided at the inner peripheral surface of the cylinder case 441 a and divides the cylinder into the cylinder opening side and the cylinder bottom surface side. A through passage 444 a through which the divided cylinder opening side and the cylinder bottom surface side are in communication is formed at a center of the valve seat portion 444. The valve member 444 supports the ball valve 442 from the cylinder opening side in a manner that the biased ball valve 442 closes the through passage 444 a. A valve seat surface 444 b is formed at the opening of the cylinder bottom surface side of the through passage 444 a and the ball valve 442 is detachably seated (in contact) on the valve seat surface 444 b.

A space defined by the ball valve 442, the biasing portion 443, the valve seat portion 444 and the inner circumferential surface of the cylinder case 441 a at the cylinder bottom surface side is referred to as a “first chamber 4A”. The first chamber 4A is filled with the brake fluid and is connected to the conduit 431 a via the port 4 a and to the conduit 422 via the port 4 b.

The control piston 445 includes a main body portion 445 a formed in a substantially columnar shape and a projection portion 445 b formed in a substantially columnar shape having a smaller diameter than the main body portion 445 a. The main body portion 445 a is arranged in the cylinder 441 in a coaxial and liquid-tight manner on the cylinder opening side of the valve seat portion 444, the main body portion 445 a being slidably movable in the axial direction. The main body portion 445 a is biased towards the cylinder opening side by means of a biasing member (not shown). A passage 445 c is formed at a substantially intermediate portion of the main body portion 445 a in a cylinder axis direction. The passage 445 c extends in the radial direction (in an up-and-down direction as viewed in the drawing) and both end portions thereof open at a circumferential surface of the main body portion 445 a. A portion of an inner circumferential surface of the cylinder 441 corresponding to an opening position of the passage 445 c is provided with the port 4 d and is formed to be recessed, which recessed space portion forms a “third chamber 4C”.

The projection portion 445 b projects towards the cylinder bottom surface side from a center portion of an end surface of the cylinder bottom surface side of the main body portion 445 a. The projection portion 445 b is formed so that the diameter thereof is smaller than the diameter of the through passage 444 a of the valve seat portion 444. The projection portion 445 b is coaxially provided relative to the through passage 444 a. A tip end of the projection portion 445 b is spaced apart from the ball valve 442 towards the cylinder opening side by a predetermined distance. A passage 445 d is formed at the projection portion 445 b so that the passage 445 d extends in the cylinder axis direction and opens at a center portion of an end surface of the projection portion 445 b. The passage 445 d extends up to the inside of the main body portion 445 a and is connected to the passage 445 c.

A space defined by the end surface of the cylinder bottom surface side of the main body portion 445 a, an outer surface of the projection portion 445 b, the inner circumferential surface of the cylinder 441, the valve seat portion 444 and the ball valve 442 is referred to as a “second chamber 4B”. The second chamber 4B is in communication with the ports 4 d and 4 e via the passages 445 d and 445 c and the third chamber 4C.

The sub-piston 446 includes a sub main body portion 446 a, a first projection portion 446 b and a second projection portion 446 c. The sub main body portion 446 a is formed in a substantially columnar shape. The sub main body portion 446 a is arranged within the cylinder 441 in a coaxial and liquid-tight manner on the cylinder opening side of the main body portion 445 a the sub main body portion 446 a being slidably movable in the axial direction.

The first projection portion 446 b is formed in a substantially columnar shape having a smaller diameter than the sub main body portion 446 a and projects from a center portion of an end surface of the cylinder bottom surface side of the sub main body portion 446 a. The first projection portion 446 b is in contact with the end surface of the cylinder bottom surface side of the sub main body portion 446 a. The second projection portion 446 c is formed in the same shape as the first projection portion 446 b. The second projection portion 446 c projects from a center portion of an end surface of the cylinder opening side of the sub main body portion 446 a. The second projection portion 446 c is in contact with the cover member 441 b.

A space defined by the end surface of the cylinder bottom surface side of the sub main body portion 446 a, an outer peripheral surface of the first projection portion 446 b, an end surface of the cylinder opening side of the control piston 445 and the inner circumferential surface of the cylinder 441 is referred to as a “first pilot chamber 4D”. The first pilot chamber 4D is in communication with the pressure decreasing valve 41 via the port 4 f and the conduit 413 and is in communication with the pressure increasing valve 42 via the port 4 g and the conduit 421.

A space defined by the end surface of cylinder opening side of the sub main body portion 446 a, an outer peripheral surface of the second projection portion 446 c, the cover member 441 b and the inner circumferential surface of the cylinder 441 is referred to as a “second pilot chamber 4E”. The second pilot chamber 4E is in communication with the port 11 g via the port 4 h and the conduits 511 and 51. Each of the chambers 4A through 4E is filled with the brake fluid. The pressure sensor 74 is a sensor that detects the servo pressure (corresponding to the “output hydraulic pressure”) to be supplied to the servo chamber 1A and is connected to the conduit 163. The pressure sensor 74 sends the detected signal to the brake ECU 6.

(Brake Actuator 53)

The first and the second master chambers 1D and 1E which generate the master cylinder hydraulic pressure (master pressure) are connected to the wheel cylinders 541 through 544 via the conduits 51 and 52 and the brake actuator 53. Each wheel cylinder 541 through 544 can apply braking force to each corresponding vehicle wheel 5FR through 5RL in response to the master pressure from the master cylinder 1. The wheel cylinders 541 through 544 form a brake device for the vehicle wheels 5FR through 5RL. In more specifically, the port 11 g of the first master chamber 1D and the port 11 i of the second master chamber 1E are connected to the well-known brake actuator 53 via the conduits 51 and 52, respectively. The brake actuator 53 is connected to the wheel cylinders 541 through 544 which are operated to perform braking operation at the wheels 5FR through 5RL.

The brake actuator 53 will be explained hereinafter representing the structure and operation regarding to one vehicle wheel (5RL) and the explanation of the other structures are omitted due to the similarity thereof. The brake actuator 53 includes a holding valve 531, a pressure decreasing valve 532, a reservoir 533, a pump 534 and a motor 535. The holding valve 531 is a normally open type electromagnetic valve and the opening and closing operation thereof is controlled by the brake ECU 6. One end of the holding valve 531 is connected to the conduit 51 and the other end thereof is connected to the wheel cylinder 544 and the pressure decreasing valve 532. In other words, the holding valve 531 serves as an input valve of the brake actuator 53. The brake actuator 53 is structured so that the flow of the brake fluid from the master cylinder 1 into the wheel cylinder 544 is interrupted by closing the holding valve 531 upon the holding mode and the pressure decreasing mode of the ABS control and the flow of the brake fluid from the master cylinder 1 into the wheel cylinder 544 is allowed by opening the holding valve 531 upon the pressure increasing mode of the ABS control.

The pressure decreasing valve 532 is a normally closed type electromagnetic valve and the opening and closing operation thereof is controlled by the brake ECU 6. One end of the pressure decreasing valve 532 is connected to the wheel cylinder 544 and the holding valve 531 and the other end thereof is connected to the reservoir 533. When the pressure decreasing valve 532 is opened, the fluid communication between the wheel cylinder 544 and the reservoir 533 is established.

The reservoir 533 is served as reserving the brake fluid and is connected to the conduit 51 via the pump 534. The suction port of the pump 534 is connected to the reservoir 533 and the discharge port is connected to the conduit 51 via a check valve “z”. It is noted here that the check valve “z” allows a fluid flow from the pump 534 to the conduit 51 (first master chamber) and restricts the flow in the reverse direction. The pump 534 is driven by the operation of the motor 535 in response to the instructions from the brake ECU 6. The pump 534 suctions the brake fluid from the reservoir 533 in which the brake fluid is reserved and returns the brake fluid into the first master chamber 1D while the ABS control, TRC (Traction Control) control, or ESC (anti-skid control) is performed. It is noted that a damper (not shown) is provided at the upstream side of the pump 534 in order to dampen the pulsation of the brake fluid ejected by the pump 534. Thus, the brake actuator 53 is provided between the master cylinder 1 and the wheel cylinders 541 through 544 and is structured to be capable of applying a target wheel cylinder which is a wheel cylinder pressure responding to a desired braking force based on the master cylinder pressure of the master cylinder 1 by means of respective holding valves and pressure decreasing valves provided corresponding respective wheel cylinders 541 through 544.

The brake actuator 53 includes a wheel speed sensor 76 which detects a wheel speed. The detected signal which indicates the wheel speed detected by the wheel speed sensor 76 is outputted to the brake ECU 6 at each vehicle wheel 5FR, 5FL, 5RR and 5RL. The detection signal which indicates the wheel speed detected by the wheel speed sensor 76 is outputted to the brake ECU 6.

In the brake actuator 53, the brake ECU 6 executes an ABS control (Anti-lock braking control) by controlling the switching over of each holding valve and the pressure decreasing valve based on the master pressure, state of wheel speed and front/rear acceleration and adjusting the brake hydraulic pressure to be applied to each wheel cylinder 541 through 544, i.e., braking force to be applied to each wheel 5FR through 5RL by operating the motor when necessary. The brake actuator 53 is a device which supplies the brake fluid supplied from the master cylinder 1 to the wheel cylinders 541 through 544 by adjusting the amount and the timing based on the instructions from the brake ECU 6. The brake actuator 53 has a function of actuator which allows the brake fluid to flow into and discharge from the master chamber 1D. In the ABS control, the brake actuator 53 executes a braking control which accompanies a brake fluid pumping back control in which the brake fluid supplied to the wheel cylinders 541 through 544 by pumping operation of the pump 534 is pumped back to the master cylinder 1 via the reservoir 533.

In the “linear mode” which will be explained later, the hydraulic pressure sent out from the accumulator 431 of the servo pressure generating device 4 is controlled by the pressure increasing valve 42 and the pressure decreasing valve 41. By the generation of the servo pressure in the servo chamber 1A, the first master piston 14 and the second master piston 15 advance to pressurize the first and the second master chambers 1D and 1E. The hydraulic pressures in the first and the second master chambers 1D and 1E are supplied to the wheel cylinders 541 through 544 from the ports 11 g and 11 i via the conduits 51 and 53 and the brake actuator 53 to apply the hydraulic pressure braking force to the vehicle wheels 5FR through 5RL.

(Brake ECU 6)

The brake ECU 6 is an electronic control unit and includes a microprocessor. The microprocessor includes an input/output interface, CPU, RAM, ROM and a memory portion such as non-volatile memory, connected with one another through bus communication.

The brake ECU 6 is connected to the various sensors 71 through 76 for controlling the electromagnetic valves 22, 23, 41 and 42 and the motor 433 and so on. The operating amount (pedal stroke) of brake pedal 10 operated by the operator of the vehicle is inputted to the brake ECU 6 from the stroke sensor 71, whether or not the operation of the brake pedal 10 by the operator of the vehicle is performed is inputted to the brake ECU 6 from the brake stop switch 72, the reaction force hydraulic pressure of the second hydraulic pressure chamber 1C or the pressure (or the reaction force hydraulic pressure) of the first hydraulic pressure chamber 1B is inputted to the brake ECU 6 from the pressure sensor 73, the servo pressure supplied to the servo chamber 1A is inputted to the brake ECU 6 from the pressure sensor 74, the accumulator hydraulic pressure of the accumulator 431 is inputted to the brake ECU 6 from the pressure sensor 75 and each wheel speed of the respective vehicle wheels 5FR through 5RL is inputted to the brake ECU 6 from each of the wheel speed sensors 76. The brake ECU 6 memorizes the two control modes, “linear mode” and “REG mode”.

(Linear Mode)

The linear mode of the brake ECU 6 will be explained hereinafter. The linear mode means a normally operated brake control. In other words, the brake ECU 6 energizes the first control valve 22 and opens the first control valve 22 and energizes the second control valve 23 and closes the second control valve 23. By this closing of the second control valve 23, the communication between the second hydraulic pressure chamber 1C and the reservoir 171 is interrupted and by the opening of the first control valve 22, the communication between the first and the second hydraulic pressure chambers 1B and 1C is established. Thus, the linear mode is a mode for controlling the servo pressure of the servo chamber 1A by controlling the pressure decreasing and pressure increasing valves 41 and 42 under the first control valve 22 being opened and the second control valve 23 being closed. Under this linear mode, the brake ECU 6 calculates the “required braking force” of the driver of the vehicle based on the operating amount of the brake pedal 10 detected by the stroke sensor 71 (displaced amount of the input piston 13) or the operating force of the brake pedal 10.

In more detail, under the state that the brake pedal 10 is not depressed, the linear mode becomes the state as explained above, i.e., the state that the ball valve 442 closes the through passage 444 a of the valve seat portion 444. Under this state, the pressure decreasing valve 41 is in an open state and the pressure increasing valve 42 is in a closed state. In other words, the communication between the first chamber 4A and the second chamber 4B is interrupted.

The second chamber 4B is in communication with the servo chamber 1A via the conduit 163 to keep the hydraulic pressures in the two chambers 4B and 1A being mutually in an equal level. The second chamber 4B is in communication with the third chamber 4C via the passages 445 c and 445 d of the control piston 445. Accordingly, the second chamber 4B and the third chamber 4C are in communication with the reservoir 171 via the conduits 414,161. One side of the pilot hydraulic pressure chamber 4D is closed by the pressure increasing valve 42, while the other side thereof is connected to the reservoir 171. The first pilot chamber 4D and the second chamber 4B are keeping at the same pressure. The second pilot chamber 4E is in communication with the first master chamber 1D via the conduits 511 and 51 thereby keeping the pressure level of the two chambers 4E and 1D mutually to be equal to each other.

From this state, when the brake pedal 10 is depressed, the brake ECU 6 controls the pressure decreasing valve 41 and the pressure increasing valve 42 based on the target friction braking force (Corresponding to the required braking force). In other words, the brake ECU 6 controls the pressure decreasing valve 41 to be in a closing direction and controls the pressure increasing valve 42 to be in an open direction.

When the pressure increasing valve 42 is opened, a communication between the accumulator 431 and the first pilot chamber 4D is established. When the pressure decreasing valve 41 is closed, a communication between the first pilot chamber 4D and the reservoir 171 is interrupted. The pressure in the first pilot chamber 4D can be raised by the highly pressurized operating fluid supplied from the accumulator 431. By this raising of the pressure in the first pilot chamber 4D, the control piston 445 slidably moves towards the cylinder bottom surface side (Rear side in FIG. 1). Then the tip end of the projecting portion 445 b of the control piston 445 is brought into contact with the ball valve 442 to close the passage 445 d by the ball valve 442. Thus the fluid communication between the second chamber 4B and the reservoir 171 is interrupted.

By further slidable movement of the control piston 445 towards the cylinder bottom surface side, the ball valve 442 is pushed towards the cylinder bottom surface side by the projection portion 445 b to thereby separate the ball valve 442 from the valve seat surface 444 b. This will allow establishment of fluid communication between the first chamber 4A and the second chamber 4B through the through passage 444 a of the valve seat portion 444. As the highly pressurized operating fluid is supplied to the first chamber 4A from the accumulator 431, the hydraulic pressure in the second chamber 4B is also increased by the communication therebetween. It is noted that the more the separated distance of the ball valve 442 from the valve seat surface 444 b becomes large, the more the fluid passage for the operating fluid becomes large and accordingly, the hydraulic pressure in the fluid passage downstream of the ball valve 442 becomes high. In other words, the more the pressure in the first pilot chamber 4D (pilot pressure), the larger the moving distance of the control piston 445 becomes and the larger the separated distance of the ball valve 442 from the valve seat surface 444 b becomes and accordingly, the hydraulic pressure in the second chamber 4B (servo pressure) becomes high. The brake ECU 6 controls the pressure increasing valve 42 so that the more the displacement amount of the input piston 13 (operating amount of the brake pedal 10) detected by the stroke sensor 71, the higher the pilot pressure in the first pilot chamber 4D becomes. In other words, the more the displacement amount of the input piston 13 (operating amount of the brake pedal 10), the higher the pilot pressure becomes and the higher the servo pressure becomes.

As the pressure increase of the second chamber 4B, the pressure in the servo chamber 1A which is in fluid communication with the second chamber 4B increases. By the pressure increase in the servo chamber 1A, the first master piston 14 advances forward and the pressure in the first master chamber 1D increases. Then the second master piston 15 advances forward also and the pressure in the second master chamber 1E increases. By the increase of the pressure in the first master chamber 1D, highly pressurized operating fluid is supplied to the brake actuator 53 which will be explained later and the second pilot chamber 4E. The pressure in the second pilot chamber 4E increases, but since the pressure in the first pilot chamber 4D is also increased, the sub piston 446 does not move. Thus, the highly pressurized (master pressure) operating fluid is supplied to the brake actuator 53 and friction brake is operated to brake the vehicle. The force advancing the first master piston 14 under the linear mode corresponds to the force corresponding to the servo pressure.

When the braking operation is released, as opposite to the above, the pressure decreasing valve 41 is open and the pressure increasing valve 42 is closed to establish the communication between the reservoir 171 and the first pilot chamber 4D. Then the control piston 445 retreats and the vehicle return to the state before depression of the brake pedal 10.

(REG Mode)

“REG mode” is a control mode in which the pressure decreasing valve 41, the pressure increasing valve 42, the first control valve 22 and the second control valve 23 are in non-energized state or a mode that the valves became the non-energized state due to a failure or the like.

At the “REG mode”, the pressure decreasing valve 41, the pressure increasing valve 42, the first control valve 22 and the second control valve 23 are not energized (not controlled) and accordingly, the pressure decreasing valve 41 is in an open state, the pressure increasing valve 42 is in a closed state, the first control valve 22 is in a closed state and the second control valve 23 is in an open state. The above non-energized state (not controlled state) continues after the brake pedal 10 is depressed.

In the “REG mode”, when the brake pedal 10 is depressed, the input piston 13 advances forward and the communication of the passage 18 is interrupted to thereby interrupt the communication between the reservoir 171 and the first hydraulic pressure chamber 1B. Under this state, since the first control valve 22 is in a closed state, the first hydraulic pressure chamber 1B is in fluid-tight (liquid-tight) state. However, since the first control valve 23 is in an open state, the second hydraulic pressure chamber 10 is in fluid communication with the reservoir 171.

It is noted here that when the brake pedal 10 is depressed, the input piston 13 advances forward to increase the hydraulic pressure in the first hydraulic pressure chamber 1B and due to the increase of the hydraulic pressure the first master piston 14 advances forward. At this state, since the pressure decreasing valve 41 and the pressure increasing valve 42 are not energized, the controlling of the servo pressure is not performed. In other words, the first master piston 14 advances forward only by a force (pressure in the first hydraulic pressure chamber 1B) corresponding to the operating force of the brake pedal 10. The volume of the servo chamber 1A becomes increased. However, since the servo pressure chamber 1A is in communication with the reservoir 171 via the regulator 44, the brake fluid is supplemented.

When the first master piston 14 advances forward, similar to the case of “linear mode”, the pressures in the first and the second master chambers 1D and 1E are increased. By the pressure increase of the first master chamber 1D, the pressure in the second pilot chamber 4E is increased. By the pressure increase of the second pilot chamber 4E, the sub piston 446 slidably moves towards the cylinder bottom surface side. At the same time, the control piston 445 slidably moves towards the cylinder bottom surface side by the pushing of the first projection portion 446 b. Then the projection portion 445 b is brought into contact with the ball valve 442 and the ball valve 442 is moved by the pushing of the projection portion 445 b towards the cylinder bottom surface side. In other words, the communication between the first chamber 4A and the second chamber 4B is established and the communication between the servo chamber 1A and the reservoir 171 is interrupted. Thus, the highly pressurized brake fluid by the accumulator 431 is supplied to the servo chamber 1A.

As stated above, in the “REG mode”, when the brake pedal 10 is depressed to a predetermined stroke by operating force, the communication between the accumulator 431 and the servo chamber 1A is established to increase the servo pressure even without assistance of control. Then the first master piston 14 advances forward more than a distance corresponding to the operating force of the driver of the vehicle. Accordingly, the highly pressurized brake fluid is supplied to the brake actuator 53 even each electromagnetic valve is under non-energized state, as long as a highly pressurized fluid exists in the accumulator 431.

(Control Example)

Next, a control example of operation of the vehicle brake device structured above will be explained with reference to the flowchart indicated in FIG. 3. The brake ECU 6 repeatedly executes the program corresponding to the flowchart above every predetermined short period of time (control cycle time).

The brake ECU 6 judges whether the ABS control is under operation or not at the step S104 every time the execution of the program is started at the step S100 in FIG. 3. The ABS control is defined to be under operation from the time after the ABS control start condition has been established until the time the ABS control end condition establishes. The ABS control is not considered to be under operation other than the time period defined above. When the ABS control is under operation, the brake ECU 6 judges “YES” at the step S104 and advances the program to the step S124. When the ABS control is not under operation, the brake ECU 6 judges “NO” at the step S104 and advances the program to the step S126 to turn the increase prohibiting flag OFF and advances the program to the step S114.

The ABS control start condition is, in detail, the state that satisfies the vehicle speed is equal to or more than a predetermined speed (for example, 5 km/h), the brake pedal 10 is operated to be depressed and the slip ratio which is a difference between the vehicle speed and the wheel speed is equal to or more than a predetermined value. When the condition is satisfied, the brake ECU 6 instructs the brake actuator 53 to decrease the pressure. Thus, the ABS control starts. During the ABC control operation, the brake ECU 6 instructs the brake actuator 53 to decrease, hold, or increase the pressure based on the wheel speed and front/rear acceleration of each wheel 5FR through 5RL so that the braking force at each wheel cylinder 541 through 544 is adjusted. Further, the ABS control end condition is, in detail, the state that satisfies for example, the depression force of the brake pedal 10 becomes zero, the vehicle speed downs to a predetermined extreme low speed or less than that, or a continuing time of the state that pressure increasing operation is being performed at all of the vehicle wheels which are the subject of the ABS control exceeds a predetermined time period.

When the brake ECU 6 judges “YES” at the step S104, the brake ECU 6 judges whether the increase prohibiting flag is ON or not at the step S124. When the increase prohibiting flag is OFF, the program goes to the step S102. At the step S102, the brake ECU 6 judges whether a predetermined time passed or not from the time the last time ABS control ended. The predetermined time is set, for example, to a time period (for example, 100 ms) from the time after the ABS control operation finished to the time when the hydraulic pressure at each wheel becomes the pressure equal to the master pressure, for example, the predetermined time is the time period during which the driver is considered to be feeling a deceleration as the deceleration that is generated corresponding to the finish of operation of the ABS control. When the predetermined time passed, the brake ECU 6 judges “YES” at the step S102 and advances the program to the step S106. When the predetermined time has not elapsed, the brake ECU 6 judges “NO” at the step S102 and advances the program to the step S122.

(Under ABS Control Operation)

The brake ECU 6 judges “YES” at the step S104, “NO” at the step S124 and “YES” at the step S102 to execute the increase of the target servo pressure (Steps S106 and S108), when the predetermined time passed since the time period of the end of the last time ABS control operation and yet the ABS control is under operation. At the step S106, the increase amount (n) which corresponds to the predetermined amount is set. At the step S108, the target servo pressure is increased by the increase amount (n). The increased target servo pressure is the target servo pressure after increase. The increase amount (n) is the increase amount of the control cycle of this time and the increase amount (n−1) is the increase amount of the control cycle of last time.

The target servo pressure is a value determined based on the operation (operating amount and operating force) of the brake pedal 10 by the driver of the vehicle and the servo pressure corresponding to the braking force required by the driver of the vehicle (hereinafter referred to as “driver requiring pressure”). This target servo pressure is set based on the operating amount (stroke) of the brake pedal 10 detected by the stroke sensor 71. The increase amount (n) is set based on the variation value of the servo pressure generated in response to the variation of the master pressure generated upon braking control (for example, ABS control) which accompanies the brake fluid pumping back control. In more detail, when the braking control which accompanies the brake fluid pumping back control in which the brake fluid supplied to the wheel cylinders 541 through 544 by the brake actuator 53 is pumped back to the master cylinder 1, for example, the ABS control is executed, upon actuation of the brake actuator 53, the brake fluid is pumped back to the master cylinder 1 side from the wheel cylinders 541 through 544 side and again the brake fluid in the master cylinder 1 side is sent to the wheel cylinders side 541 through 544. This control cycle is repeatedly performed and the first master piston 14 (and the second master piston 15) repeats the advancement and retreatment movements in a short period of time. Then the volume of the servo chamber 1A is decreased or increased to frequently change the actual servo pressure therein. It is preferable to set the increase amount (n) so that the minimum variation value of the actual servo pressure does not fall below the target servo pressure. The increase amount (n) can be calculated from the variation value of the actual servo pressure calculated in advance by an experimental work.

Further, the increase amount (n) may be set based on the control dead zone of the controlling (feedback controlling) of the pressure increasing valve 42 and the pressure decreasing valve 41. In other words, the increase amount (n) is preferably set to a value so that the lower limit value of the control dead zone (lower limit value of the pressure increase dead zone) does not fall below the target servo pressure. It is noted here that the control dead zone is the area in which the controlling of the pressure increasing valve 42 and the pressure decreasing valve 41 is prohibited and when the deviation of the actual servo pressure relative to the target servo pressure is within the area, the controlling of the pressure increasing valve 42 and the pressure decreasing valve 41 is prohibited. In other words, during the ABS control, the actual servo pressure is frequently varied and since the controlling of the pressure increasing valve 42 and the pressure decreasing valve 41 cannot follow such frequent variation of the actual servo pressure, the control dead zone is provided to include the variation of the actual servo pressure.

Still further, the increase amount (n) is preferably set in response to the brake fluid amount (total flow amount) supplied from the master cylinder 1. In detail, the number of the control subject wheels for the ABS control is four (4) at most and the volume of brake fluid to be supplied corresponds to the volume of four wheel cylinders. In the ESC control, the number of the control subject wheels is one (1) and the volume of brake fluid to be supplied corresponds to the volume of one wheel cylinder. As explained, the more the total flow amount of the brake fluid to be supplied to the wheel cylinders, the larger the variation of the master pressure becomes and accordingly, it is preferable to set the increase amount (n) to be sufficiently large.

(Under Release Operation after ABS Control Ended)

After the end of the ABS control, if the brake pedal 10 is being released, the brake ECU 6 judges “NO” at the step S104 and turns the increase prohibiting flag OFF at the step S126 then judges “YES” and “NO” at the steps S114 and S116, respectively to gradually decrease the “target servo pressure after increase” at the step S118.

At the step S114, the brake ECU 6 judges whether the increase amount (n) of this time is equal to or less than a predetermined value “c”. The predetermined value “c” is set to be a very small value, approximately close to zero. At the time immediately after the end of ABS control, the increase amount (n) is a larger value and the brake ECU 6 judges “YES” at the step S114. On the other hand, when some time passed after the end of ABS control, the increase amount (n) becomes small and when the value becomes approximately zero, the brake ECU 6 judges “NO” at the step S114 and the increase amount is set to be zero at the step S128.

At the step S116, the brake ECU 6 judges whether the operator (driver of the vehicle) released the brake pedal 10 from the depression or not. In more detail, the brake ECU 6 obtains the operating amount of the brake pedal 10 from the stroke sensor 71 and when the operating amount is decreased the brake ECU 6 judges that the brake pedal 10 has been released from the depression operation. When the operating amount is increased, the brake ECU 6 judges that the brake pedal 10 has been further depressed and when the operating amount is kept constant, the brake ECU 6 judges that the depression of the brake pedal 10 has been maintained constant.

At the step S118, after the execution of the ABS control (the braking control which accompanies the brake fluid pumping back control) has been finished, the target servo pressure which has been increased during the execution of the ABS control is decreased based on a ratio of the increase amount which has been increased during the ABS control relative to the target servo pressure at the time when the execution of the ABS control finished.

In concrete, the brake ECU 6 calculates the increase amount (n) after the ABS control ended from the mathematic formula (M1) as follow: Increase amount(n)=Driver requiring pressure of this time×Increase amount during ABS control/Driver requiring pressure at the time ABS control ended  [M1]

The driver requiring pressure of this time is calculated based on the operating amount of the brake pedal 10 detected by the stroke sensor 71 at the control cycle of this time. The increase amount during ABS control is the increase amount calculated during the ABS control of the latest time. The driver requiring pressure at the time ABS control ended is calculated based on the operating amount of the brake pedal 10 detected by the stroke sensor 71 at the time the ABS control ended. For example, in the third chart in FIG. 4, when the ratio of (Driver requiring pressure at the time ABS control ended):(Increase amount during ABS control) is a:b, the increase amount (n) can be represented as the driver requiring pressure of this time×(b/a).

It is noted here that the brake ECU 6 may be structured such that the brake ECU 6 decreases the target servo pressure after increase in response to the decrease of the operating amount of the brake pedal 10. For example, the brake ECU 6 may calculate the increase amount by multiplying the increase amount during the ABS control by the decrease ratio of the operating amount at the current time relative to the operating amount at the time the ABS control ended.

When the increase amount (n) is decreased and becomes approximately zero, the brake ECU 6 judges “NO” at the step S114 and sets the increase amount to be zero at the step S128. Thus, the target servo pressure after increase becomes approximately equal to the target servo pressure.

(During Depression Increasing or Holding after the ABS Control Ended)

After the ABS control ended, when the depression of the brake pedal 10 is increasing or is being maintained constant, the brake ECU 6 judges “NO” “YES” and “NO” at the steps S104, S114 and S116, respectively to maintain the increase amount to be constant (Step S120). At the step S120, the brake ECU 6 changes the increase amount (n−1) at the control cycle of last time to the increase amount (n) at the control cycle of this time. Thereafter, the brake ECU 6 advances the program to the step S108.

(In the Case that the ABS Control Started within a Predetermined Time Period after the ABS Control Ended)

When the ABS control started within a time period from the end of the last ABS control to a time when a predetermined time passed, the brake ECU 6 judges “YES” at the step S104, “NO” at the step S124 and “NO” at the step S102. At the step S122, the brake ECU 6 turns the increase prohibiting flag ON and thereafter at the step S130, prohibits the increase of the target servo pressure. Then the brake ECU 6 advances the program to the step S108. The “during ABS control” which has been temporarily in “increase prohibited” is judged to “YES” at the step S104 and “YES” at the step S124 and the program goes to the step S130 to prohibit the increase until the ABS control ends.

(Feedback Control of Servo Pressure)

The brake ECU 6 executes the increase of the target servo pressure at the step S108. In detail, the brake ECU 6 calculates the target servo pressure based on the operating amount of the brake pedal 10 detected by the stroke sensor 71 and then calculates the target servo pressure after increase by adding the increase amount calculated as above, to the target servo pressure.

The brake ECU 6 executes the feedback control of the servo pressure at the step S110. The brake ECU 6 executes the control (feedback control) of the pressure increasing valve 42 and the pressure decreasing valve 41 so that the actual servo pressure detected by the pressure sensor 74 becomes the target servo pressure after increase calculated as above. Thereafter, the brake ECU 6 advances the program to the step S112.

(Explanation by Using Time Chart)

The time chart shown in FIG. 4 will be explained. In FIG. 4, the first chart indicates whether the ABS is “during ABS control” or not, the second chart indicates the stroke of the brake pedal 10, the third chart indicates the target servo pressure, the target servo pressure after increase and the actual servo pressure and the forth chart indicates the wheel cylinder pressure. At the time t1, the depression (operation) of the brake pedal 10 starts. From the time t1 to the time t2, the depression increasing operation of the brake pedal 10 is performed. The stroke of the brake pedal 10 is also increasing in response to the depression increasing operation. Since the target servo pressure is set based on the stroke of the brake pedal 10, the target servo pressure is also increasing in response to the depression increasing operation. The actual servo pressure is increasing and the master pressure is increasing due to the increase of the actual servo pressure. The wheel cylinder pressure is increasing due to the increase of the master pressure.

From the time t2 to the time t4, the depression amount of the brake pedal 10 is maintained constant (holding operation). At this time, the stroke of the brake pedal 10 is maintained constant and the target servo pressure is maintained constant. The actual servo pressure, the master pressure and the wheel cylinder pressure are maintained constant.

However, when the ABS control starts at the time t3, until the ABS control ends, during the ABS control (from the time t3 to the time t4), the target servo pressure is increased by the increase amount (n). In other words, the target servo pressure after increase is set. In concrete, the target servo pressure after increase is calculated by adding the increase amount (n) to the target servo pressure. The third chart in FIG. 4 shows the target servo pressure with a bold solid line, the target servo pressure after increase with a bold broken line and the actual servo pressure with a fine broken line.

The actual servo pressure is feedback-controlled so that the actual servo pressure becomes the target servo pressure after increase (Steps S104 through S110) and accordingly, compared to the non-increase case, the actual servo pressure is increased by the increase amount worth as a whole. Thus, during the ABS control, a relatively high servo pressure is supplied to the servo chamber 1A. As a result, the without drop of the master pressure, and eventually drop of the wheel cylinder pressure, a deceleration which responds to the desired requiring deceleration can be generated.

The explanation will be made by comparing the case of non-increase. When the increase is not performed, when the brake actuator 53 is actuated upon execution of the ABS control, the brake fluid is returned from the wheel cylinder 541 through 544 side to the master cylinder 1 side and again is sent to the wheel cylinder 541 through 544 side from the master cylinder 1 side. These are repeatedly performed and the master piston 14 is repeatedly retreated and advanced with a short time period and accompanied by this operation of the master piston 14, the volume of the servo chamber 1A is increased and decreased to frequently change the actual servo pressure. In other words, as shown in the third chart of FIG. 4 with the fine solid line, the actual servo pressure surges within the control dead zone (indicated with the bold one-dot line) set having the target servo pressure at the central portion thereof. At this time, there are cases where the actual servo pressure is lower than the target servo pressure. As a result, the actual master pressure drops more than the master pressure corresponding to the target servo pressure and as shown with a broken line in the fourth chart of FIG. 4, the wheel cylinder pressure drops to decrease the actual deceleration relative to the requiring deceleration.

On the other hand, according to the embodiment of the invention, similar to the case of non-increase, when the brake actuator 53 is actuated upon the execution of ABS control, the master pressure surges and accompanied by this the actual servo pressure also surges. However, since the target servo pressure is increased to the target servo pressure after increase, the range of surging is raised by the increase amount as a whole compared to the case of non-increase. In other words, as shown with the fine broken line in the third chart of FIG. 4, the actual servo pressure surges within a control dead zone (bold two-dot line) which is set having the target servo pressure after increase at the central portion thereof. The actual servo pressure at this time would not drop lower than the target servo pressure. As a result, the actual master pressure would not drop lower than the master pressure corresponding to the target servo pressure and as shown with a solid line at the fourth chart of FIG. 4, the wheel cylinder pressure would not drop and a desired wheel cylinder pressure can be supplied and accordingly, the deceleration in response to the desired requiring deceleration can be generated. It is noted here that at the third chart of FIG. 4, the target servo pressure after increase is indicated with the bold broken line and the actual servo pressure is indicated with the fine broken line.

From the time t4 to the time t5, the depression release operation of the brake pedal 10 is performed and at this time, the stroke of the brake pedal 10 is decreasing in response to the depression release operation of the brake pedal 10. The target servo pressure is set based on the stroke of the brake pedal 10 and accordingly, decreases in response to the depression release operation. Further, the target servo pressure after increase which has been increased during ABS control is gradually decreased so that the ratio of (Driver requiring pressure at the time ABS control ended):(Increase amount during ABS control) becomes the ratio of a:b. (Step S118). The target servo pressure after increase the amount of which began decreasing finally agrees approximately with the target servo pressure.

As apparent from the forgoing explanation, according to the embodiment, the brake ECU 6 (vehicle control device) executes the control of the pressure increasing valve 42 and the pressure decreasing valve 41 so that the actual servo pressure detected by the pressure sensor 74 (servo pressure sensor) becomes the target servo pressure and controls so as to increase the target servo pressure by the increase amount (predetermined amount), while the brake actuator 53 is executing the braking control (for example, ABS control) which accompanies the brake fluid pumping back control in which the brake fluid supplied to the wheel cylinders 541 through 544 is pumped back to the master cylinder 1 by the pump 534 (built-in pump). (Steps S104 through S108).

According to the structure above, while the braking control which accompanies the brake fluid pumping back control, such as for example, ABS control is performed, the target servo pressure is increased by the increase amount (predetermined amount) and accordingly, the actual servo pressure can be increased in response to the increase amount. Accordingly, during the pressure increasing operation of the ABS control, when the brake fluid is sent to the wheel cylinder 541 through 544 side from the master cylinder 1 side due to the advancement of the master piston 1 (14), a relatively high servo pressure can be supplied to the servo chamber 1A. As a result, the without drop of the master pressure, and eventually drop of the wheel cylinder pressure, a deceleration which responds to the desired requiring deceleration can be generated. In other words, a vehicle control device which can surely generate a desired requiring deceleration in the vehicle brake device without receiving any influence of the delay of responsiveness of servo pressure generation can be provided.

Further, the brake ECU 6 sets the increase amount (predetermined amount) based on the variation value of the servo pressure which is accompanied by the master pressure variation generated upon the braking control which accompanies the brake fluid pumping back control. Accordingly, the during the braking control which accompanies the brake fluid pumping back control (such as during ABS control), the increase amount of the target servo pressure can be properly set so that a relatively high servo pressure can be surely supplied to the servo chamber 1A.

After the execution of the braking control which accompanies the brake fluid pumping back control has been finished, the brake ECU 6 decreases the target servo pressure (the target servo pressure after increase) which has been increased during the execution of the braking control which accompanies the brake fluid pumping back control is decreased based on a ratio (a/b) of the increase amount (predetermined amount) which has been increased during the braking control which accompanies the brake fluid pumping back control relative to the target servo pressure at an end of the execution of the braking control which accompanies the brake fluid pumping back control. (Step S118). According to the feature above, after the execution of the braking control (such as ABS control) which accompanies the brake fluid pumping back control has been finished, the target servo pressure can be gradually changed to suppress the uncomfortable feeling which the operator of the brake pedal 10 feels.

After the execution of the braking control which accompanies the brake fluid pumping back control has been finished, the brake ECU 6 decreases the target servo pressure which has been increased during the execution of the braking control which accompanies the brake fluid pumping back control is decreased in response to (based on) a decrease of an operating amount of the brake pedal 10. According to the feature above, after the execution of the braking control (such as ABS control) which accompanies the brake fluid pumping back control has been finished, the target servo pressure can be gradually changed to suppress the uncomfortable feeling which the operator of the brake pedal 10 feels.

The brake ECU 6 prohibits an increase of the target servo pressure by the increase amount (predetermined amount) until a predetermined time period passes from the end of the execution of the braking control which accompanies the brake fluid pumping back control. (Step 102,122) According to the feature above, when the braking control which accompanies the brake fluid pumping back control is repeatedly executed for a short period of time (for example, when a vehicle is running on a road, the surface of which has different friction coefficient alternatively, the execution and non-execution of the ABS control are repeatedly performed) a new target servo pressure increase operation is not performed until the predetermined time period passes from the time when the execution of the braking control which accompanies the brake fluid pumping back control finished, even the braking control which accompanies the brake fluid pumping back control is executed. Thus, an unlimited increase of the target servo pressure can be prevented.

According to the structure of the embodiment explained above, the brake ECU 6 prohibits the increase of the target servo pressure by the increase amount (predetermined amount) until a predetermined time period passes from the time when the execution of the braking control which accompanies the brake fluid pumping back control finished. However, instead of this, a total increase amount of the target servo pressure is limited to an increase amount upper limit value when the increase of the target servo pressure is executed. According to the feature above, as shown in FIG. 5, the brake ECU 6 after setting the increase amount (n), applies the set increase amount (n) when the set increase amount (n) is less than the increase upper limit value and applies the increase upper limit value when the set increase amount (n) is equal to or more than the increase upper limit value.

According to the above feature, when the ABS control (braking control which accompanies the brake fluid pumping back control) is repeatedly executed for a short period of time (for example, when a vehicle is running on a road, the surface of which has different friction coefficient alternatively, the execution and non-execution of the ABS control are repeatedly performed) a target servo pressure increase operation is not performed even if the predetermined time period passes from the time when the execution of the braking control which accompanies the brake fluid pumping back control finished, when the total increase amount of the target servo pressure reached limited to the increase amount upper limit value. Thus, an unlimited increase of the target servo pressure can be prevented. It is noted here that the total increase amount is increased based on the reference of the last time increase amount (target servo pressure after increase) when this time increase is performed before the last time increase becomes zero.

Further, as the braking control which accompanies the brake fluid pumping back control, in addition to the ABS control, other controls, such as ESC control or Traction Control in which the brake fluid supplied to the wheel cylinders 541 through 544 is pumped back to the master cylinder 1 by the pump 534 of the brake actuator 53 can be applicable. In this case, the target servo pressure is set in response to the brake pedal 10 operation (operating amount, operating force) in the ABS control, and is set in response to the braking force to be applied to the wheel which is the objective of the control (braking force application objective) in the ESC control or the Traction Control.

According to the invention, the structure that the servo pressure is applied to the rear side of the first master piston 14 is adapted, but the invention is not limited to this structure and another structure having a master piston that slidable moves within the master cylinder 1 and generates the master cylinder hydraulic pressure in response to the servo pressure. Further, the target servo pressure can be set based on the brake operating force of the brake pedal 10 instead of the operating amount of the brake pedal 10. In such case, a sensor which detects the operating force may be added. 

The invention claimed is:
 1. A vehicle control device applicable to a vehicle brake device which includes; a master cylinder having a master piston configured to be driven to move by a servo pressure in a servo chamber and in which movement of the master piston changes a master pressure in a master chamber; a servo pressure generating device formed by a high pressure source, a pressure increasing control valve disposed between the high pressure source and the servo chamber for controlling a flow of a brake fluid from the high pressure source to the servo chamber and a pressure decreasing control valve disposed between a low pressure source and the servo chamber for controlling the flow of the brake fluid from the servo chamber to the low pressure source for generating the servo pressure in the servo chamber in response to an operation of a brake operating member by a driver of a vehicle; a servo pressure sensor configure to detect the servo pressure; a wheel cylinder configure to apply a braking force to a vehicle wheel in response to the master pressure from the master cylinder; and a brake actuator disposed between the master cylinder and the wheel cylinder and structured at least so that the brake fluid supplied to the wheel cylinder is pumped back to the master cylinder by a built-in pump, the brake actuator being used for a braking control for controlling a braking force generated by the wheel cylinder, wherein, the vehicle control device is configured to control the pressure increasing control valve and the pressure decreasing control valve so that an actual servo pressure detected by the servo pressure sensor becomes a target servo pressure; is configured to judge whether or not the brake actuator is executing the braking control which accompanies a brake fluid pumping back control in which the brake fluid supplied to the wheel cylinder is pumped back to the master cylinder by the built-in pump, and to control so as to increase the target servo pressure by a predetermined amount when the vehicle control device judges that the brake actuator is executing the braking control which accompanies the brake fluid pumping back control in which the brake fluid supplied to the wheel cylinder is pumped back to the master cylinder by the built-in pump; and after the execution of the braking control which accompanies the brake fluid pumping back control has been finished, the target servo pressure increased during the execution of the braking control which accompanies the brake fluid pumping back control is decreased based on a ratio of the predetermined amount increased during the braking control which accompanies the brake fluid pumping back control relative to the target servo pressure at an end of the execution of the braking control which accompanies the brake fluid pumping back control.
 2. The vehicle control device according to claim 1, wherein, the predetermined amount is set based on a variation value of the servo pressure derived from a variation of the master pressure generated upon an execution of the braking control which accompanies the brake fluid pumping back control.
 3. The vehicle control device according to claim 1, wherein, after the execution of the braking control which accompanies the brake fluid pumping back control has been finished, the target servo pressure increased during the execution of the braking control which accompanies the brake fluid pumping back control is decreased in response to a decrease of an operating amount of the brake operating member.
 4. The vehicle control device according to claim 1, wherein, an increase of the target servo pressure by the predetermined amount is prohibited when the braking control which accompanies the brake fluid pumping back control is started within a time period from an end of the last brake control to a time when a predetermined time has passed from the end of the last brake control.
 5. The vehicle control device according to claim 1, wherein, a total increase amount of the target servo pressure is limited to an increase amount upper limit value when the increase of the target servo pressure is executed. 